The present invention relates to a switching system for interconnecting a plurality of computer user terminals or workstations each having user interface devices, including a keyboard, a video display unit, and a cursor control device or mouse (KVM), with a plurality of computers in a computer network, allowing a user to access any one or more of said computers from the user interface devices of a single terminal or workstation. It is denoted xe2x80x9chigh endxe2x80x9d because of the potentially large number of computers which may be interconnected with the system.
A keyboard-video-mouse (KVM) switching system for selectively interconnecting a single workstation with a plurality of remotely located computers, a xe2x80x9clow-endxe2x80x9d system, is described for example in U.S. Pat. No. 5,499,377 (Designed Enclosures, Inc.) and such systems are available from Cybex Inc., and other suppliers. xe2x80x9cHigh endxe2x80x9d KVM systems, in which multiple workstations may be selectively interconnected with any one of multiple computers via a computerized switching hub are available from, inter alia, Cybex Inc., Apex PC Solutions Inc., Rose Electronics Inc., Lightwave Communications Inc., C-C-C Group Limited. These systems greatly facilitate system administration in a local area network from a single workstation, which may be located in a different room or building from interconnected computers such as servers in a large client server network. Interconnecting cabling needs are also reduced. A typical high end KVM switching system is described in U.S. Pat. No. 5,721,842 (Apex). Signal conditioning interface units receive keyboard and mouse signals from a workstation and generate serial digital data packets which are transmitted to a switching hub comprising a central crosspoint switch. The crosspoint switch routes the keyboard/mouse packet to another signal conditioning interface unit coupled to the selected remote computer. Analogue video output signals from the remote computer are transmitted via central analogue crosspoint switching arrangement to the workstation, so that it appears to the workstation user that there is a direct connection between the workstation keyboard, video monitor and mouse to any one of 32 remotely-located computers. The switching hub comprises a master Central Processing Unit (CPU), a plurality of identical transmit/receive cards, a plurality of switch cards each comprising a 16xc3x9716 digital crosspoint switch and a separate 16xc3x9716 analogue crosspoint switch, a digital backplane and a separate analogue backplane. Such a system has to be powered down for removal or upgrading of cards, and a failure on one switch card or in the master CPU will cause the whole system to fail. In contrast, the present invention provides a high end KVM system with distributed control, i.e. without a master CPU, and in which all cards and components are xe2x80x9chot-swappable,xe2x80x9d a significant advantage which allows for simple maintenance and updating of the system to interconnect more workstations and computers, without any system down time.
U.S. Pat. No. 5,884,096 (Apex) describes a similar high end KVM switching system.
The present invention provides a switching system for interconnecting a plurality of computer user terminals (1-16), having user interface devices including a keyboard (1b), a video display unit (1a) and a cursor control device (1c), with a plurality of computers (201-328) in a computer network, allowing a user to access any one or more of said computers from the user interface devices or a single terminal, comprising a switching hub (40) for routing keyboard and cursor control signals transmitted from any one (1) of the terminals (1-16) to a selected computer (201), and for routing video signals received from the said computer to said one of the terminals, said signals being in both digital and analogue form, a user interface module (17-32) for receiving said transmitted keyboard and cursor control signals, coupled between said plurality of computer user terminals (1-16) and said switching hub (40), a computer interface module (51-178) for receiving said received video signals, coupled between said plurality of computers (201-328) and said switching hub (40), characterized in that the physical architecture of the switching hub (40) is a modular system comprising a plurality of switch modules (41), each module comprising an analogue transmitter (43) circuit and/or an analogue receiver (42) circuit, each including an analogue crosspoint switching arrangement, a programmable digital circuit (44) for handling digital data signals and including a digital crosspoint switching arrangement, and a backplane (45) interface between the said analogue (42, 43) and digital (44) circuits.
In another aspect, the invention provides a switching hub (40) comprising a plurality of removable and hot swappable switch modules (41) each with its own crosspoint switching arrangement (402, 501, 502) and central processing unit (400), each module comprising an analogue transmitter (43) circuit and/or an analogue receiver (42) circuit, a programmable digital circuit (44) for handling digital data signals and a backplane (45) interface between the said analogue (42, 43) and digital (44) circuits.
In a further aspect, the invention provides a switching hub (40) comprising a crosspoint switching arrangement (402, 501, 502), including an analogue crosspoint switch (501, 502) with a switch topology based on a switched transconductance architecture.
In a still further aspect, the invention provides a switching hub (40) which is a modular system comprising a plurality of switch modules (41), each module comprising a separate analogue transmitter (43) circuit or an analogue receiver (42) circuit, each including an analogue crosspoint switching arrangement, a separate programmable digital circuit (44) for handling digital data signals and including a digital crosspoint switching arrangement, and a backplane (45) interface between the said analogue (42, 43) and digital (44) circuits, said analogue circuit embodying stripline structures for video bus channel paths.
The invention also provides methods of switching KVM signals in a KVM system, using the system described, and in the manner as herein set forth.
Modular System
In its preferred embodiment, the invention creates a truly modular system, which is very easily scaleable to the desired system, in terms of connecting more users and computers as needs change, by simply adding more modules to the system. This is achieved by providing switch modules, or packs of cards, for transmit and receive modes, providing access to a pre-determined number of user- or computer interfaces of the system. In the described embodiment, a system is provided where each switch module can handle sixteen video channels, and with nine modules loaded, the system will allow sixteen users to control 128 computers in a non-blocking way.
Economic System Architecture
In its preferred embodiment, the invention reduces costs of design and manufacture by splitting each switch module into an analogue card and a digital card, wherein the digital card is a common card which may be used interchangeably for both transmit and receive modes, i.e. bundled either with an analogue receiver or transmitter card.
Hot Swap
In its preferred embodiment, the invention provides a fully xe2x80x9chot-swappablexe2x80x9d modular KVM system. Every single removable module in the system may therefore be hot swappable, i.e. may be plugged or unplugged in a powered on condition. This includes; power-supplies, fan modules, all cards, control panel.
CAN-bus as Internal Communication
In its preferred embodiment, the invention provides communication between all cards based on a Controller Area Network (CAN) bus, for example; all switching information, system information, update information for the main CPU, update information for the programmable logic devices, control information.
Synchronization Signals
Whereas the analogue cards are for distributing video signals, the preferred embodiment of the invention provides a digital card for handling vertical and horizontal synchronization signals (HS and VS) exclusively for the video channel, and the external communication. VS and HS signals are not encoded onto the analogue color video signals (e.g. green and blue) as in the prior art, U.S. Pat. No. 5,884,096 (Apex).
Video Quality
In its preferred embodiment, the invention improves transmitted video signal quality, without any loss of quality when a large number of computers are connected to the system. This is achieved by a combination of features, a common object of which is to preserve the integrity of the video signals and minimize crosstalk at every stage during transmission through the system, to avoid for instance xe2x80x9cghostingxe2x80x9d on screen from interference of other video channels in the system. These features include, but are not limited to the following:
Choice of Crosspoint Switch
An analogue crosspoint switch topology based on xe2x80x9cswitched transconductance architecturexe2x80x9d is preferred over the more common xe2x80x9cbilateral mosfet (or CMOS) switchxe2x80x9d type of device, described for instance in U.S. Pat. No. 5,884,096 (Apex). In the described embodiment of the present invention, the particular crosspoint switch used consists of an array of 128 transconductance input stages organized as eight 16:1 multiplexers with a common, 16-line analogue input bus. Each multiplexer is basically a folded-cascode high-speed voltage feedback amplifier with sixteen input stages. This architecture results in a low-power, large matrix crosspoint switch with high input resistance, low input capacitance and wide bandwidth without the use of additional input buffers. Bi-lateral mosfet (or CMOS) switches on the other hand suffer from significant parasitic capacitance and finite ON resistance since they are not internally buffered. This reduces overall bandwidth and causes variation in bandwidth as outputs are added or removed from a driving input.
Backplane Design
Controlled impedance xe2x80x9ctriplinexe2x80x9d techniques have been used in the design of the analogue video bus portion of the backplane in order to optimize signal integrity, channel bandwidth and crosstalk separation. Adjacent channel crosstalk separation is enhanced by interleaving adjacent channel paths in an alternate tri-plate stnipline structure. i.e. all even channels are carried in one stripline structure and all odd channels are carried in an other. Expanding on the above technique additional stnipline structures may be used to further enhance the separation between channels thus further improving the crosstalk separation.
Backplane Interconnect Design
In order to maintain maximum system bandwidth and optimal crosstalk separation, special consideration has been given to the design of interconnectors at the backplane. A specific pin assignment is used with the connector array in order to minimize the crosstalk separation between channels, in a technique which creates a pseudo-coaxial cavity for each analogue signal path within the mated connector body thereby resulting in optimal crosstalk separation. In the embodiment described, a suitable connector for this technique is from the HDM plus range manufactured by Teradyne, Inc.
Additional Noise Reduction Measures
In order to reduce conducted noise from the digital portion to the analogue circuits, galvanic isolation has been incorporated in all interface paths between the digital card and the analogue card. This has been achieved through the use of optocouplers in all digital signal paths between the analogue printed circuit board (PCB) and digital PCB. In the embodiment described, a suitable optocoupler is part HCPL-0531, supplied by Hewlett Packard, Inc.
Redundant Power Supplies
In its preferred embodiment, the invention provides a KVM switching system with a fully redundant power supply, having at least two independent power supply systems. If one power supply fails, the other one will guarantee a stable system which will go on working without interruption.
FPGA Crosspoint Switch Arrangement
In its preferred embodiment, the invention provides a programmable logic device, such as a field programmable gate array (FGPA) for switching the synchronization signals. In the described embodiment, there are advantageously two bi-directional 16 by 16-crosspoint switches, both switched simultaneously for distributing horizontal and vertical synchronization signals always together on one channel. These crosspoint switches are preferably controlled by the main CPU. The logic device is preferably accessed by a data bus, an address bus and some control signals. This interface may be compatible to a standard microcontroller interface or a serial control link. This device is preferably programmable from the main CPU of the system. Advantageously, it is adapted to be automatically updated when the firmware of the CPU is updated.
Low Voltage Differential Transceiver (LVDS) Backplane Drivers
Differential LVDS drivers/receivers are used for the backplane. This reduces electromagnetic interference (EMI) and reduces crosstalk to other signals.
Remote Firmware Update
Advantageously, all programmable electronic devices may be reprogrammed or updated from a remote location. Alternatively, updates could be performed by computers with a serial, parallel, LAN, Internet, Infra-red and radio controlled transmission. The system could be configured via Internet.
System Monitoring Via Control Panel
Advantageously, the control panel may be used for updating the whole system. The update information is distributed via the CAN bus internally and the external command bus distributes this information to other switch modules. It is possible to update cards in other units connected to the system. Another advantageous use of the control panel is to configure the system and do administrative work, including debugging the system.
Single Unshielded Twisted Pair (UTP) Category 5 (CATS) Cable Transmission
A single CATS transmission cable may be used to interconnect workstation and computer interfaces to the KVM switching system hub. Such a cable is of known construction, e.g. as described in U.S. patent applications Ser. Nos. 60/043,085, 60/045,608, 09/073,178, 08/971,223, 08/971,224, all assigned to Cybex Inc.
Flash Upgradable Firmware
Firmware in the system is preferably flash memory upgradeable. The system starts up from a boot ROM/EPROM and looks for a newer firmware version in the flash memory. If there is a newer version, the system executes commands from the flash memory.